Extended statistics and function-based indexes

About a year ago I’ve discovered nice feature of Oracle 10gR2 CBO: to overcome an issue with calculated selectivity for predicates on multiple columns, it can use DISTINCT_KEYS of the available index. Couple of weeks ago the bug fix mentioned in the OTN thread actually helped to solve a performance issue of a query. And about a week ago I found that this fix doesn’t work with function-based indexes. So, this post is about it.

Control file sequential read

There was a thread recently on the OTN forum (it’s currently down, that’s why I’m writing in the blog; here is a stale version of the page from Google cache; at the time of writing this version had 1 comment) about reasons for control file sequential read accounted to particular query.